Secondary Electrical Insulation Coatings Containing Nanomaterials

ABSTRACT

Use of the barrier property effect of nanomaterials to improve the electrical insulation resistance and corrosion protection strength properties of electromagnetic devices. The beneficial effects are realized with nanomaterial loadings of 1-20%, and preferably between 1-5%, parts by weight of coating resins. Nanomaterials include, but are not limited to, silica, alumina, zirconia, and antimony pentoxide, which are dispersed either directly into a coating, or pre-dispersed in a carrier appropriate to the solvent of the resin system. The rheology of the resin system is not significantly altered which would otherwise affect processing of the resins for their intended applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending applicationSer. No. 11/252,921 which was filed on Oct. 18, 2005, is entitled “UseOf Nanomaterials In Secondary Electrical Insulation Coatings”, and whichis incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND

This invention relates to electromagnetic devices; and, moreparticularly, to the use of nanomaterials in insulation coatings forthese devices.

Organic resin compositions are used as coatings for the mechanical,electrical and environmental-resistance they impart to electromagneticdevices. The coatings provide a mechanical strength, electricalinsulation, and environmental protection for improved long-termdurability of the devices, as well as increasing the quality of thefinal product. Some of these beneficial properties can be improved bythe addition of inorganic fillers such as silica, calcium carbonate,alumina, etc. However, a problem with the current state of thistechnology is that the inorganic materials used in the coatings do notalways remain suspended in the coatings, resulting in a non-homogeneousmixture. When the coatings are applied to the devices, areas of weaknessresult that, in turn, can cause failure of a device.

This current state of the art raises several issues related to thehandling of the coating, its agitation (to produce homogeneity beforeapplication) and its pumping, and concerns about the homogeneity of boththe applied liquid and the resulting cured film. Prior approachesemployed to address these problems have focused on the use of fumedsilica used to increase viscosity and improve suspension of theinorganic materials. But, in some instances, use of these agentsproduced undesirable results because of rheological changes which occurand cause inconsistencies in the applied coatings.

SUMMARY

The present invention is directed to coatings utilizing the barrierproperty effect of nanomaterials to improve the electrical insulationresistance and corrosion protection of electromagnetic devices; withoutthe coating having the non-homogeneity problems described above. Thesebeneficial effects are realized with nanomaterial loadings of 1-20%, andpreferably between 1-5%, parts by weight to the coating resin. Thenanomaterials used include, but are not limited to, silica, alumina,zirconia, and antimony pentoxide. These nanomaterials are dispersedeither directly into a coating, or pre-dispersed in a carrierappropriate to the solvent of the resin system being modified. Theresulting formulations benefit from the fact that anti-settling agentsneed not be incorporated in the mixture to keep the inorganic materialsuspended in the coating. A further benefit is that the rheology of theresin system is not significantly altered which would otherwise affectthe processing of the resins in their intended applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing the viscosity of Epoxy-unsaturated polyestercopolymer with and without nanomaterials over time;

DETAILED DESCRIPTION

The following detailed description illustrates the invention by way ofexample and not by way of limitation. This description will clearlyenable one skilled in the art to make and use the invention, anddescribes several embodiments, adaptations, variations, alternatives anduses of the invention, including what we presently believe is the bestmode of carrying out the invention. As various changes could be made inthe above constructions without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

In accordance with the present invention, barrier property effects ofnanomaterials are used to improve the electrical insulation resistanceand corrosion protection properties of electromagnetic devices coatedwith a coating resin incorporating the nanomaterials, whilesimultaneously avoiding the homogeneity problems previously discussed.To achieve these desired results, inorganic materials in the 1-150nanometer (nm) range are used in formulating the coating resins appliedto the devices. By contrast, the size of inorganic particles in current,state-of-the-art filler systems is on the order of 3000-4500 nm.Suitable chemistries for the coating resin include, but are not limitedto, unsaturated polyesters, epoxies, urethanes, waterborne polyesters,epoxy emulsions, organic solvent borne alkyds, acrylated andmethacrylated urethanes, acrylated and methacrylated epoxies, acrylatedand methacrylated polyols, and acrylated and methacrylated vegetableoils. The desired effects are achieved using nanomaterial loadings ofbetween 1-20% part by weight, and preferably between 1-5% part byweight, of a nanomaterial to the resin. Nanomaterials that can be usedinclude, but are not limited to, silica, alumina, zirconia, and antimonypentoxide. Those skilled in the art will understand that the resultingcoatings can be tailored to meet specific performance requirements for adevice by the inclusion of an appropriate amount of a nanomaterial or acombination of nanomaterials. One important advantage of the coatings ofthe present invention is that the rheology of the resin system is notsignificantly altered; although, in some instances, there is an increasein the viscosity of the resulting mixture. Overall, though, processingof the resins for their intended applications is not materiallyaffected.

With respect to the use of nanomaterials, their small particle sizemeans that a given amount of material is more evenly distributedthroughout the resin, creating a more tortuous path which is harder forcorrosive agents to penetrate. Further, the particles being in closeproximity to each other promotes dissipation of any electrical charge,thereby leading to improved electrical properties of a device in whichthe coating is incorporated.

The barrier effect resulting from use of the nanomaterials producessignificant results in the coatings made in accordance with theinvention. For example, the improved electrical and corrosion resistanceproperties referred to above occur even though lower amounts ofinorganic nanomaterials are used in producing a coating than when usingother inorganic filler materials. The coatings also have an equalabrasion resistance, even though, again, lower amounts of inorganicnanomaterials are used in the coating. Third, some of the new coatingsmay have a lower viscosity than current coatings. All of these featuresserve to provide greater flexibility in processing options for thecoating, while achieving desired performance characteristics for thecompleted device.

During preparation, the nanomaterials are either dispersed directly intoa coating resin, or the nanomaterials are pre-dispersed in a carrierappropriate to the solvent of the resin system being modified. Asignificant advantage of the resulting formulations is that viscosityincreasing anti-settling or suspension agents do not need to be added tothe resulting mixture to keep the nanomaterial suspended in the mixture.A second advantage is that homogeneity of the coating mixture isachieved and maintained with a minimal amount of agitation of themixture as compared to that required for conventional coating mixtureshaving inorganic fillers.

Nanomaterial modified organic coatings are applied using the sameprocesses currently used in the industry. These include, but are notlimited to, dip and bake, trickle, vacuum/pressure impregnation, rollthrough, spray, and vacuum impregnation. In addition, coatings made inaccordance with the present invention are cured using currentlyavailable methods. Such curing methods include, but are not limited to,gas-fired ovens, resistance heating, infrared radiation heating,chemical catalyzation and ultraviolet (UV) radiation curing. Regardlessof the method of application, coatings incorporating a nanomaterial morereadily flow into the areas of the electromagnetic device being coated,since the inorganic nanomaterial is of a smaller particle size than theinorganic filler materials used in conventional coatings. Further, withrespect to UV curing processes, coatings made in accordance with thepresent invention have been found to exhibit an improved opticalclarity. This facilitates use of UV induced curing processes that cannotnow be used because of the presence of organic fillers in currentcoatings.

The following refers to Tables 1 and 2. TABLE 1 Standard Filledunsaturated polyester (UPE) System I System II Commercial 70 99 97Polyester A Silica, 2.9 microns 30 0 0 Nanoalumina, 50 nm 0 1 3

TABLE 2 Standard Waterborne Polyester (WBPE) System III CommercialWaterborne 100 97 Polyester Nanoalumina, 150 nm 0 3

Preparation:

Referring to Table 1, a standard, filled unsaturated polyester (UPE)coating was prepared by dispersing 30 parts by weight (pbw) of silica in70 pbw of a UPE resin using a high speed dispersion process until theresulting mixture was homogeneous. In addition, two nano-modified UPEsamples were prepared. The first, referred to as System I in Table 1,was prepared by adding 1 pbw of a nanomaterial (50 nm nanoalumina) to 99pbw of the UPE resin and then mixing until a homogenous mixture wasachieved. The second, referred to as System II in Table 1, was preparedby adding 3 pbw of the nanomaterial (50 nm nanoalumina) to 97 pbw of theUPE resin and again mixing until a homogeneous mixture was achieved.

Referring to Table 2, a nano-modified waterborne polyester (WBPE)coating, referred to as System III in the Table, was prepared by adding3 pbw of a nanomaterial (150 nm nanoalumina) to 97 pbw of WBPE andmixing until a homogenous mixture was achieved. Because the polyester isa waterborne polyester, the nanoalumina was predispersed in water. Thispredispersed nanoalumina/water solution was added to the WBPE material.Stated differently, the nanoalumina was added as a dispersion in waterto reach a final concentration of 3%.

Physical properties of the representative formulations are listed inTable 3. TABLE 3 Standard UPE Standard UPE Filled UPE w/NanomaterialInorganic Loading, % 0 30 3 Viscosity, 25° C., Cp 100-200 150-250150-400 Density, 25° C. 1.09 1.30 1.09

As seen in Table 3, the nanomaterial loaded UPE had a viscosity similarto the standard filled UPE even though it was made using only 10% of theamount of inorganic material used in the standard filled UPE. This gavethe nanomaterial loaded UPE of the present invention a density that wasabout 17% less than the density of the standard filled UPE and aboutequal to the standard UPE. An unsaturated polyester which uses fumedsilica to prevent settling of inorganic fillers has a viscosity of inthe range of about 8000 to about 12000 centipoise. As can be seen, theuse of the nanomaterial provides for a composition having a viscositywhich is substantially less than the viscosity of a polyester resinthickened with fumed silica. Rather, the polyester with nanomaterialshas a viscosity that is similar to the viscosity of the standardpolyester.

Test results of formulation examples are listed in Table 4 in whichcorrosion and settling ratings of 1-10 for corrosion are based on 1being worst, and 10 best. TABLE 4 Standard System System Filled UPE I IIPulse Endurance, min. 3200 4 >6000 Helical coil bond 23 15 20 strength,lbs Dielectric strength, vpm 3000 3500 4300 Corrosion 6 1 9 Settling 1 99

TABLE 5 Standard WBPE System III Pulse Endurance, minutes 28 56 Helicalcoil bond strength, lbs 12 12 Dielectric strength, vpm 5400 3100Corrosion 10 10 Settling 10 9

As seen from Tables 4 and 5, the System I and II (nanomaterial loaded)UPE'S had significantly better settling properties—that is, theinorganic material did not settle, but remained substantially suspendedin the resin. The System I and II coatings also had higher dielectricstrengths; and the System II coating had a substantially higher pulseendurance than the standard filled UPE. The System III similarly had asubstantially higher pulse endurance than did the standard WBE.

In another set of tests, concentrated dispersions of nanoalumina (50 nm)and nanosilica (20 nm) in an epoxy unsaturated polyester were preparedby SW mill technique. These were used to make versions of precatalyzedepoxy-unsaturated polyester copolymer at 3% and 5% nanoparticles. Testresults comparing the epoxy-unsaturated polyester copolymer without thenanomaterials (standard) with the nanomaterial containingepoxy-unsaturated polyester copolymer are set forth below in Tables 6and 7. The test data for the “standard” is set forth in both Tables 6and 7. TABLE 6 Nanoalumina in epoxy unsaturated polyester StandardExperimental Formula 1 Experimental Formula 2 Epoxy- Epoxy-unsaturatedEpoxy-unsaturated unsaturated polyester copolymer polyester copolymerpolyester with 3% nanoalumina with 5% nanoalumina copolymer (50 nm) (50nm) Viscosity  569 634  670 125 C gel  10.1 10.3   9.8 Bond Strength,lbs @  28.5 29.4   29.8 25° C. Bond Strength, lbs @   5.4 8.2   8.4 150°C. Dielectric Strength, 4938 4597  1369 volt/mil Film thickness 1 mil0.8   0.9 Pulse Endurance  500′ >6000′

TABLE 7 Nanosilica in epoxy unsaturated polyester ExperimentalExperimental Standard Formula 3 Formula 4 Epoxy- Epoxy-unsaturatedEpoxy-unsaturated unsaturated polyester copolymer polyester copolymerpolyester with 3% nanosilica with 5% nanosilica copolymer (20 nm) (20nm) Viscosity cP  569 606  623 125 C gel  10.1 9.9′   10.4′ BondStrength,  28.5 29.9   32.0 lbs @ 25° C. Bond Strength,   5.4 6.5   6.2lbs @ 150° C. Dielectric 4938 4967  4694 Strength, volt/mil Filmthickness 1 mil 0.8   0.8 Pulse  500′ >6000′ Endurance

The nanoalumina and nanosilica in epoxy unsaturated polyester formulassettled badly, so a lot of work was put into finding different additivesto help keep the particles suspended. By using a commercially availabledispersing agent, the nanoparticles remained suspended long enough towork with.

Table 8, below, shows data comparing Epoxy-unsaturated polyestercopolymer loaded with 5% nanosilica (20 nm) with Epoxy-unsaturatedpolyester copolymer containing no nanosilica. TABLE 8 Epoxy unsaturatedpolyester copolymer with 5% Nanosilica Epoxy-unsaturated polyestercopolymer Epoxy-unsaturated without polyester copolymer nanomaterialswith 5% nanosilica Specific gravity 1.07 g/cm³ 1.10 g/cm³ Gel time @125° C. (minutes) 13.7 11.4 Dielectric Strength, v/mil 1294 1241Thickness, mils 17 18 Tan Delta @ 155° C., 60 Hz, 0.0130 0.1425 500 VTan Delta @ 180° C., 60 Hz, 0.0380 0.1425 500 V Accelerated aging @ 50°C., viscosity (cP) @ 25° C. At 0 hours 653 856 At 24 hours 669 879 At 48hours 694 933 At 72 hours 719 971 At 96 hours 741 1014 At 168 hours 8071136

As seen from the results tabulated in Table 8, the addition of thenanosilica reduced the gel time for the coating, even at similar coatingthicknesses. The Tan Delta ratio (the ratio of the storage modulus tothe loss modulus values) at 155° C. and at 180° C. was substantiallyincreased by the addition of the nanosilica. Also, as shown graphicallyin FIG. 1, the nanosilica loaded epoxy-unsaturated polyester copolymerset substantially faster than the epoxy-unsaturated polyester copolymerwithout nanomaterials. The equation for the trendline for the two curvesis shown on the chart of FIG. 1. As seen, the slope of the nanomaterialloaded resin has a slope of about 1.7 whereas the resin without thenanomaterial has a slope of about 0.9. In fact, after 168 hours, theepoxy-unsaturated polyester copolymer without nanomaterials had not evenreached the viscosity of the epoxy-unsaturated polyester copolymer withnanomaterials.

Results for polyester with antimony pentoxide nanoparticles (added as acommercially available 40% dispersion) in a standard unsaturatedpolyester resin are shown below in Table 9. To make the mixture, acommercially available 40% dispersion of antimony pentoxide in polyesterwas added to the polyester resin. A sufficient amount of the dispersionwas added to the polyester resin to produce the 1%, 3% and 5% by weightmixtures set forth below in Table 9. TABLE 9 Unsaturated UnsaturatedUnsaturated polyester polyester Standard polyester with with withunsaturated 1% antimony 3% antimony 5% antimony polyester pentoxidepentoxide pentoxide Viscosity, cP 200 Not tested 315 427 Pulse 4 Nottested Not tested >6000 Endurance, minutes Helical 20.6 14.7 13.2 12.4Coil bond strength, lbs

As can be seen from Table 9, as the amount of antimony pentoxide addedto the polyester was increased, the viscosity of the mixture increased,the pulse endurance of the mixture increased, and the helical coil bondstrength of the mixture decreased. The lower bond strengths thatresulted are believed to be due to the fact that the polyester used issaturated and unreactive with the unsaturated polyester used in thetests.

Results for water reducible polyamide imide (PAI) with nanoaluminaparticles are shown below in Table 10. The coating made from thismixture blistered badly when cured at 200° C. This prevented any testingon cured properties, but did not have any bearing on the properties setforth below in Table 10. It has been suggested that it might be possibleto bake the coating at 100° C. to remove the bulk of the water and thencure at 200° C. Water is a by-product of the cure, so blistering isstill a possibility. TABLE 10 Water Water reduced PAI at 20% reduced PAIat 20% nonvolatile material with nonvolatile material 5% nanoaluminaViscosity, cP 233 162 % nonvolatile material 20.1 20.8 Appearance Cleardark brown Milky dark brown liquid liquid

In view of the above, it will be seen that we have provided ananomaterial containing coating, the properties of which surpass theproperties of currently available organic resin coatings. Importantly,the coating composition does not require viscosity increasinganti-settling agents to keep the nanomaterial suspended in the mixture.Further, the inclusion of the nanomaterial in the mixture does notsignificantly altering the rheology of the coating for use in aparticular application.

1. A coating composition for an electromagnetic device to improve theelectrical insulation resistance and corrosion protection properties ofthe device, the coating composition comprising a substantiallyhomogenous mixture of a commercially available coating resin materialand an inorganic nanomaterial; the nanomaterial being added to the resinmaterial by between approximately 1-20% part by weight of thecomposition.
 2. The coating composition of claim 1 in which thenanomaterial is an inorganic material in the range of 1-150 nanometers.3. The coating composition of claim 2 in which the nanomaterial ischosen from the group consisting of silica, alumina, zirconia, antimonypentoxide and combinations thereof.
 4. The coating composition of claim1 in which the nanomaterial comprises between approximately 1-5% part byweight of the composition.
 5. The coating composition of claim 1 inwhich the resin material is a standard filled unsaturated polyester(UPE) coating material.
 6. The coating composition of claim 1 in whichthe resin material is a water borne polyester (WBPE) coating material.7. The coating composition of claim 1 in which the nanomaterial isdispersed directly into the resin material.
 8. The coating compositionof claim 1 in which the nanomaterial is pre-dispersed into a carrierappropriate for the resin material with which the nanomaterial is mixed.9. The coating composition of claim 1 in which the barrier effectresulting from use of the nanomaterial improves electrical and corrosionresistance properties of the coating using lower amounts of thenanomaterial than a coating produced using a standard inorganic fillermaterial.
 10. The coating composition of claim 9 in which the barriereffect resulting from use of the nanomaterial further improves theabrasion resistance of the coating.
 11. The coating composition of claim10 in which the barrier effect resulting from use of the nanomaterialproduces a coating having a low viscosity relative to systems wherefumed silica is used to prevent settling of fillers, thereby providingflexibility in processing options for the coating.
 12. The coatingcomposition of claim 11 in which the coating has a viscosity of lessthan 1000 centipoise.
 13. A coating composition for an electromagneticdevice to improve the electrical insulation resistance and corrosionprotection properties of the device, the coating composition consistingof a substantially homogenous mixture of a commercially availablecoating resin material and an inorganic nanomaterial; the nanomaterialbeing added to the resin material by between approximately 1-20% part byweight of the composition; the nanomaterial being chosen from the groupconsisting of silica, alumina, zirconia, antimony pentoxide andcombinations thereof; and the resin material being chosen from the groupconsisting of unsaturated polyesters, epoxies, urethanes, waterbornepolyesters, epoxy emulsions, organic solvent borne alkyds, acrylated andmethacrylated urethanes, acrylated and methacrylated epoxies, acrylatedand methacrylated polyols, acrylated and methacrylated vegetable oils,and combinations thereof.
 14. The coating composition of claim 13 inwhich the nanomaterial is an inorganic material in the range of 1-150nanometers.
 15. The coating composition of claim 13 in which thenanomaterial comprises between approximately 1-5% part by weight of thecomposition.
 16. A process for producing a coating composition for anelectromagnetic device to improve the electrical insulation resistanceand corrosion protection properties of the device; the processcomprising: formulating a coating resin using a commercially availableresin material; adding to the resin material between approximately 1-20%part by weight of a nanomaterial; mixing the resin material andnanomaterial together until a homogeneous composition is achieved. 17.The process of claim 16 in which between approximately 1-5% part byweight of the nanomaterial is added to the resin material.
 18. Theprocess of claim 16 in which the nanomaterial is an inorganic materialin the range of 1-150 nanometers.
 19. The process of claim 16 whereinthe nanomaterial is chosen from the group consisting of silica, alumina,zirconia, antimony pentoxide and combinations thereof.
 20. The processof claim 16 in which the resin material is a standard filled unsaturatedpolyester (UPE) coating material.
 21. The process of claim 16 in whichthe resin material is a water borne polyester (WBPE) coating material.22. The process of claim 16 wherein the step of adding the nanomaterialto the resin comprises dispersing the nanomaterial directly into theresin.
 23. The process of claim 16 wherein the step of adding thenanomaterial to the resin comprises pre-dispersing the nanomaterial intoa carrier appropriate for the resin material with which the nanomaterialis mixed and mixing the pre-dispersed nanomaterial with the resin.